It has long been common practice in the farm and construction equipment fields to arrange the engine so that it provides both tractive effort for the vehicle and hydraulic power for operation of hydraulically actuated auxiliary equipment carried on or towed by the vehicle. One of the major problems, particularly with some types of construction equipment, such as loaders for example, has been splitting the power from the engine between the tractive effort load and the hydraulic load. Some operator skill in the operation of the equipment has always been required to properly apportion this splitting of the power. An attempt to ease the demands on the operator is disclosed in U.S. Pat. No. 3,789,943, issued Feb. 5, 1974 to K. W. Kampert and K. E. Houtz, wherein the engine operated with the speed control lever continuously in the maximum position between a governed high idle speed and peak torque speed in response to the load imposed on the engine. The speed of such a "constant throttle" engine is independent of ground speed and a modulated clutch was utilized to control clutch slip and hence ground speed. The engine was sized to handle both the maximum hydraulic load and the maximum tractive effort without stalling. Under such conditions, the response of the hydraulic system is sluggish because flow is reduced and the travel speed of the vehicle is slowed for any given drive train ratio because the engine has been lugged down to a speed that is at or just above stall. While such an arrangement permits operation with less operator judgment and skill required, such judgment and skill are still necessary for maximum productivity.
A power split which is set and invariable does not provide efficient use of the available engine power. In a loader, for example, as the bucket is being filled, the vehicle is driven forward into the material while the boom arms are raised slightly and the bucket is rolled back to "break-out" the load into the bucket. During such a maneuver, the power requirement for tractive effort is high but the hydraulic power requirement is relatively low since hydraulic power is a function of both pressure and flow. While the pressure may be at the maximum permitted within the system, the movements of the bucket and boom are small and relatively slow necessitating a small flow. With an even split between traction and hydraulic load set, e.g. 50% to each, only half of the engine's power would be available for traction with the other half available for the hydraulic load. However, the tractive effort could use more power, while the hydraulic load does not require 50% of the engine's power. Conversely, once the bucket is loaded, the boom arms must be raised rapidly and the bucket simultaneously rolled back to maintain it level as the loader is driven to discharge the load, such as into a truck. The heavy load in the bucket and the speed of movement of the boom arms requires a large flow at a relatively high pressure resulting a large hydraulic power requirement. The tractive effort at such time is, for the most part, only rolling resistance. The engine will not be lugged down by the tractive effort load, and would therefore, be capable of devoting a larger portion of its power capability to the hydraulic load.
It is therefore, an object of this invention to provide a hydraulic system which automatically reduces the hydraulic load in response to the engine being lugged down.
It is also an object of this invention to provide a hydraulic system which is responsive, which minimizes the requirements for operator judgment and skill, and which is efficient in operation.
It is also an object of this invention to provide such an improved hydraulic system for a vehicle having a "constant" throttle engine arrangement and which removes a substantial portion of the hydraulic load from the engine when the engine's speed is above its peak torque speed.
It is a further object of this invention to provide a hydraulic system which is responsive to reductions in the engine speed to reduce the hydraulic load on the engine while maintaining a responsive hydraulic system when required.
It is also an object of this invention to provide a vehicle with an engine driving both the tractive effort power train and a hydraulic load with a means for automatically supplying a larger portion of the engine's power to the power train under certain conditions and to the hydraulic load under other conditions.